Heretofore, in the operation of conventional molding machines, it has been common practice to inject molten material through the narrow passages of nozzles and mold cavities with core pins both in closed fixed positions. This procedure causes material stresses which necessitate the use of high clamping forces to prevent the molds from flashing and also requires considerable energy to generate the necessary processing injection pressures. The narrow nozzle passages are required to quickly separate the melt stream therein from the solidifying melt in the mold cavity so the hollow article can be released from the mold as early as possible. Workers in the art have further refined this technique by positioning individual shut-off nozzles in each mold cavity to shorten the time for the hot melt to solidify. However, the apertures of these shut-off nozzles are sufficiently restrictive to also require high injection pressure for filling the mold cavities. Unfortunately, the excessive frictional heat generated by these well-known techniques effects the melt quality and raises the melt temperature which in turn lengthens the cooling cycles.
U.S. Pat. Nos. 4,243,620 and 4,324,541, issued to Motosacoche, disclose a method and apparatus wherein large nozzle orifices are brought into registry with the bottom orifices of mold cavities. Core pins disposed in the apparatus are retractable during filling of the mold cavities. These features permit the filling of the cavities with molten material under low pressure at significant energy savings. Upon completion of the metering phase, the nozzles are shifted out of registry. The core pins or punches are then moved in the direction of the mold cavity bottoms or dies and compress the molten material into the final configuration of the desired hollow article or preform. Although this technique has proven to be useful, the drawback therein resides in the need for neck bushings with sufficient clearance to allow easy movement of the core pins. This clearance and the normal wear and tear of the bushings cause the core pins to deflect, thereby raising the risk of causing non-uniform side walls and defective sealing surfaces of the preforms or hollow articles. Due to the constant rubbing of the nozzle sealing surfaces against the mold cavity bottoms, the spring-loaded injection nozzle plates require frequent production interruptions, so necessitating the dismantling of the mold cavity blocks and the cleaning and lubricating of the moving contact surfaces.
U.S. Pat. Nos. 4,717,324, 4,775,308, 4,863,369 assigned to Husky, and 4,990,301 assigned to Continental PET Technologies disclose methods and related apparatus wherein each mold cavity has a single or multi-layer nozzle and a stationary hot runner system which meters one or several molten materials to the same nozzles via rotating spool valves and a plurality of manifold segments. The narrow nozzle passages require high pressures and, consequently, high clamping forces for the molten material to enter and pack out in the individual mold cavities to form the final product. The rotating spool valves of this type of apparatus can only open and close the passages for the molten material but cannot redirect the same to non-aligned exit ports. The shooting pots are built into the manifold segment and are individually monitored and post-adjusted. In the proposed invention, the opening and closing of the individual material passages is carried out through combined linear movements of common multi-passage distribution spools. In addition, these distribution spools can direct molten material not only from one but from several transfer reservoirs into one common mold cavity recipient via their circumferential and linear perpendicular radial passage channels. While the high pressure shooting pots in the aforementioned patents form directly a finished article, the unison movements of the transfer housings in the manifold assembly away and towards stationary displacement plugs serve to fill the transfer reservoirs with molten material, to convey the same at high velocity into the expanded mold cavities and, subsequently, condense the same molten material around fixed-position core pins into finished hollow articles. While the shooting pots in the aforementioned patents are directly post-adjusted for any volume correction, in the proposed invention compensation rods, located in the melt passages leading to the transfer reservoirs, preadjust indirectly the molten material volume prior to entering the same.
U.S. Pat. Nos. 4,330,257 to Husky and 4,786,455 to Continental Group disclose a method and an apparatus wherein square-shaped turrets rotate in 90 degree intervals within the machine platens of injection molding machines to form, cool and extract hollow articles and preforms. The drawback of this method and apparatus is that it is required to function within four stages which does not always permit the most optimum processing cycle.
U.S. Pat. No. 4,395,222 assigned to the Broadway Companies discloses a method wherein a molten material is conveyed from a central inlet sprue with a plurality of central runners located in a spiral configuration on the periphery of fixed-position bushings to a plurality of outlet gates. These same outlet gates intersect again with a second set of bushings with a plurality of central runners leading to the outlet gates connected with the mold cavity bottoms. These fixed-position bushings are heated internally, a procedure which is well known in the art. Although the runners in the primary and secondary cylinders are of a balanced arrangement, high injection pressures and, consequently, higher machine clamping forces are required to convey the molten material from one central inlet sprue through intersecting runners to the closed mold cavities.
An object of the present invention was to eliminate such limitations by positioning primary and secondary distribution spools in a cascading manner within the manifold, so permitting them to function like multi-stage hydraulic solenoid valves to direct, redirect, combine, or block the flow of molten material or materials simultaneously from the continuous extruding plasticizer to the plurality of transfer reservoirs or housings and from there to the plurality of mold cavities. In this arrangement, the runners are reduced to a minimum length, so permitting conveyance of the molten material at low pressures to the individual mold cavities and the total elimination of cavity nozzles.
It is a further object of the present invention to replace individual rotating spool valves, pin-type shut-off nozzles and straight-through mold cavity nozzles with common distribution spools which are shifted laterally to open, close, or redirect, via the circumferential flow passages, the molten material from the plasticizing unit into mold cavities via transfer reservoirs. It is still another object of the present invention to release the hollow articles or preforms by indexing or shuttling the core pins in a horizontal or vertical plane outside the mold clamps of the molding machines, to reduce the cycle times by holding the hollow articles or preforms longer in imminent contact with the cooling core pins, compared to systems in which robots reach in and out between the open mold halves to collect preforms in tubular cooling sleeves and by choosing the optimum number of intermittent cooling stations.
Although the foregoing compression, injection, co-injection molding and cooling methods and apparatuses have proven successful, the proposed technique results in enhancing the wall concentricity of the hollow articles and preforms, reducing the maintenance and downtimes by eliminating the cavity nozzles, increasing the production flexibility with directional distribution spools which cannot only open and close the melt passages but also redirect the molten material within the same manifold block to different center distances through lateral movements, where articles and preforms can be transferred on rotating or shuttling tables within a multitude of stations according to the different processing conditions.